1. Field of the Invention
The invention relates to a display device using a display medium the state of which is changed in accordance with an applied electric field, and more particularly to a liquid crystal display device in which a liquid crystal is used as a display medium.
2. Description of the Related Art
Conventionally, a segment liquid crystal display device using a nematic liquid crystal is widely used as, for example, a display unit of a watch or an electronic calculator. By contrast, a matrix liquid crystal display device using a nematic liquid crystal is used as a display unit of a word processor, a computer, or a navigation apparatus, and hence the market of such a liquid crystal display device is growing. Such liquid crystal display devices are very thinner and lighter than other display devices such as a CRT, and smaller in power consumption than the other display devices. In the liquid crystal display devices, furthermore, a full-color image can be easily attained. Therefore, the demand for the liquid crystal display devices is expanding in application fields which are wider than those of such other display devices. For example, the liquid crystal display devices are used as a display unit of a personal computer, various kinds of monitor apparatuses, a portable television apparatus, or a display unit of a camera.
A matrix liquid crystal display device includes a liquid crystal panel in which a plurality of pixels are arranged in a matrix form, and a liquid crystal driver which supplies an electric signal to the liquid crystal panel. In each of the pixels, a liquid crystal is sandwiched between a flat pixel electrode and a flat counter electrode. Among matrix liquid crystal display devices, particularly, an active matrix liquid crystal display device in which an active element is used as a switching element is frequently used. For example, the active element is realized by a thin film transistor (hereinafter, often abbreviated as xe2x80x9cTFTxe2x80x9d).
A liquid crystal panel of a prior art active matrix liquid crystal display device using TFTs is structured in the following manner. The liquid crystal panel includes in addition to the plurality of pixels, a main substrate and an counter substrate which transmit light, reference signal lines, TFTs the number of which is equal to the total number of the pixels, a plurality of scanning signal lines, and a plurality of gradation signal lines. Counter electrodes of all the pixels are arranged in a matrix form on one face of the counter substrate, and electrically connected to one another via the reference signal lines. The counter electrodes of all the pixels, and the reference signal lines are integrally formed into a single thin film of a conductive material which can be opposed to the pixel electrodes of all the pixels, i.e., into a common electrode.
The pixel electrodes of all the pixels are arranged on one face of the main substrate in a matrix form. The scanning signal lines are arranged on the one face of the main substrate so as to pass the peripheries of the pixel electrodes and be parallel to the row direction of the pixel arrangement. The gradation signal lines are arranged on the one face of the main substrate so as to be parallel to the column direction of the pixel arrangement. The TFTs are arranged on the one face of the main substrate. In each of the TFTs, the drain terminal is connected to one of the pixel electrodes, the gate terminal to one of the scanning signal lines, and the source terminal to one of the gradation signal lines. In the case where the liquid crystal display device can display a color image, furthermore, a color filter is disposed on the main substrate or the counter substrate. The scanning signal lines perpendicularly intersect with the gradation signal lines on the main substrate. At each of the intersections of the signal lines, the two kinds of signal lines are electrically insulated from each another so as to prevent a short circuit from occurring. The liquid crystal panel is structured as described above. In the specification, the above-described structure of the liquid crystal panel, i.e., the structure in which the counter electrodes of all the pixels are connected to the reference signal lines is referred to as xe2x80x9ccurrent structure.xe2x80x9d
The liquid crystal driver for the liquid crystal display device including the active matrix liquid crystal panel of the current structure supplies a scanning signal for driving the TFTs, to the TFTs through the scanning signal lines. During a period when each of the TFTs is driven, i.e., that when transmission of an electric signal between the source and drain terminals of the TFT is enabled, the liquid crystal driver supplies a display signal for defining the display state of the pixel including the pixel electrode which is connected to the TFT, to the pixel electrode via the gradation signal lines and the TFT. Furthermore, the liquid crystal driver always supplies a predetermined reference signal to the common electrode. The scanning signal and the gradation signal are pulsating signals of a voltage variable with time. In the case where the liquid crystal driver performs the so-called line inversion driving, the reference signal is a pulsating signal, and, in the case where the liquid crystal driver performs the so-called dot inversion driving, is a steady signal in which the voltage is always maintained to a predetermined level. As a result, in accordance with the voltage applied between the pixel electrode and the common electrode, the state of the liquid crystal between the electrodes is determined.
The liquid crystal panel of the thus configured prior art active matrix liquid crystal display device has the structure in which the scanning signal lines perpendicularly intersect with the gradation signal lines on the main substrate. In the liquid crystal panel, therefore, a failure such as that the signal lines of two kinds are short-circuited at the intersection may easily occur. As a result, the production yield of the prior art liquid crystal display device tends to be lower than that of a liquid crystal display device of another configuration.
In order to solve the problem, U.S. Pat. No. 4,694,287 discloses a liquid crystal panel having the so-called counter source structure. The liquid crystal panel of an active matrix liquid crystal display device of the prior art using TFTs and having the counter source structure is structured in the following manner. The liquid crystal panel of the counter source structure includes in addition to the plurality of pixels, an counter substrate and a main substrate which are optically transparent, gradation signal lines, TFTs the number of which is equal to the total number of the pixels; scanning signal lines, and reference signal lines.
Counter electrodes of all the pixels are arranged in a matrix form on one face of the counter substrate. The gradation signal lines are arranged on the one face of the counter substrate so as to pass the peripheries of the counter electrodes and be parallel to the column direction of the pixel arrangement. The counter electrodes of two or more of all the pixels which constitute one arbitrary column of the arrangement are electrically connected to an arbitrary one of the gradation signal lines which passes the vicinity of the column. The arbitrary gradation signal line, and all the counter electrodes connected to the signal line are integrally formed so as to constitute a single strip-like thin film piece which can be opposed to the electrodes of the pixels, and which is made of an electrically conductive material, i.e., a column electrode. As a result, a plurality of column electrodes are arranged on the one face of the counter substrate.
The pixel electrodes of all the pixels are arranged on the one face of the main substrate in a matrix form. The scanning signal lines and the reference signal lines are arranged on the one face of the main substrate so as to pass the peripheries of the pixel electrodes and be parallel to the row direction of the pixel arrangement. The TFTs are arranged on the one face of the main substrate. In each of the TFTs, the drain terminal is connected to one of the pixel electrodes, the gate terminal to one of the scanning signal lines, and the source terminal to one of the reference signal lines. The gradation signal, the scanning signal, and the reference signal are supplied to the gradation signal lines, the scanning signal lines, and the reference signal lines, respectively. The liquid crystal panel of the counter source structure is structured as described above.
Japanese Unexamined Patent Publication JP-A 4-219735 (1992) discloses a configuration for, in a liquid crystal panel of the counter source structure, preventing a so-called DC-level shift from occurring. In the liquid crystal display device disclosed in the publication, a capacitor is interposed between a reference potential supply bus line and a display electrode, i.e., between the reference signal line and the pixel electrode. Japanese Unexamined Patent Publication JP-A 7-20495 (1995) discloses a configuration for, in a liquid crystal panel of the counter source structure, eliminating capacitive coupling which may be produced by a column electrode on an counter substrate and a reference signal line on a main substrate. In the liquid crystal display device disclosed in the publication, a transparent electrode which is opposed to a plurality of pixel electrodes via a liquid crystal layer, i.e., the column electrode is configured by a plurality of first transparent electrodes which are opposed only to the plurality of pixel electrodes, respectively, and an electrically conductive layer through which the first transparent electrodes are connected to one another, and which is smaller in width than the first transparent electrodes.
Among regulations relating to an image display device which is to be used as a display unit of an information apparatus, there are standards for EMI (unwanted radiation) of high-frequency waves. Such standards for regulating EMI are originally set with the objective of protecting a radio apparatus, and differently defined in countries. Recently, there arises a fear that, in addition to EMI of high-frequency waves, a so-called leakage low-frequency electromagnetic field may adversely affect the human body. Under such circumstances, regulations for a leakage low-frequency electromagnetic field are set in the countries of northern Europe. Such regulations are expanding to many countries in the world. As one of regulations for a leakage low-frequency electromagnetic field from an image display device, TCO standard is widely known. The TCO standard is a standard conforming to measurement standard MPR-II for a VDU (Visual Display Unit) which is set by SWEDAC (Swedish board for technical accreditation). In the TCO standard, it is defined that a leakage low-frequency electromagnetic field is measured in accordance with Swedish standard SS436 14 90 and IEEE 1140-1994.
Since standards for a leakage low-frequency electromagnetic field of an image display device are set as described above, a liquid crystal display device which is to be used as an image display device for an information apparatus must be designed so that the leakage low-frequency electromagnetic field meets the standards. In order to comply with this, for example, a liquid crystal display device is structured so that a film for shielding an electromagnetic field is applied to the surface of a liquid crystal panel. Japanese Unexamined Patent Publication JP-A 5-61019 (1993) discloses a technique of reducing electromagnetic field radiation from a display panel of an AC-driven flat display device. In a liquid crystal display panel disclosed in the publication, an electrode for reducing electromagnetic field radiation is disposed in the periphery of the panel, and a voltage which is opposite in polarity to an alternating voltage that is to be supplied to a common electrode in the panel is applied to electrode for reducing electromagnetic field radiation.
The inventor of the present invention has measured a leakage low-frequency electromagnetic field, with respect to prior art liquid crystal display devices of the current structure and the counter source structure in which a countermeasure for reducing a leakage low-frequency electric field is not taken (hereinafter, such a liquid crystal display device is often referred to as xe2x80x9cuntreated LCDxe2x80x9d), in accordance with measurement standard MPR-II described above, and compared measurement results with the TCO standard. From the results, it is expected that a leakage low-frequency electric field of an untreated LCD has the following general features.
The results of the measurement on an untreated LCD of the current structure have revealed that, when the frequency of a signal supplied to the LCD is in band I, the low-frequency magnetic field and the low-frequency electric field are set within the allowable range of the TCO standard, and that, when the frequency of the supplied signal is in band II, the low-frequency electric field is hardly set within the allowable range of the TCO standard. Based on the measurement results and considering that the frequency of a signal supplied to a liquid crystal panel is approximately in a range of from 15 kHz or higher to 55 kHz, it is expected that a leakage low-frequency electric field in a liquid crystal display device is caused mainly by a voltage change of a signal supplied to a component on the counter substrate.
The results of the measurement on an untreated LCD of the counter source structure have revealed also that, when the amplitude waveform of the AC component of the reference signal is opposite in phase to that of the AC component of the gradation signal, the low-frequency electric field is weaker as the amplitude of the reference signal is higher. Based on the measurement results, it is expected that, when a signal which is opposite in phase to a signal supplied to a component on the counter substrate is supplied to a component on the main substrate, an effect of canceling the signals occurs to weaken the leakage low-frequency electric field of the liquid crystal display device. From the measurement results, it has been revealed that, in the untreated LCDs of the two kinds of structures, the leakage low-frequency electric field has a dependency on the size of the panel. Namely, in the untreated LCD, the leakage low-frequency electric field is stronger as the liquid crystal panel is larger. Based on the measurement results, it is expected that the leakage low-frequency electric field of a liquid crystal display device is stronger as the area of a component which is on the counter substrate and to which a signal is to be input is larger.
On the basis of the measurement results, it has been proposed that, in a prior art liquid crystal display device of the current structure, the dot inversion driving be used in place of the line inversion driving in order to set the leakage low-frequency electric field within the allowable range of the TCO standard, because of the following reason. In the case where the line inversion driving is used, the reference signal that is supplied to a component on the counter substrate is a pulsating signal in which the voltage is changed so as to assist the gradation signal that is supplied to a component on the main substrate. When the line inversion driving is used in the liquid crystal display device, therefore, it becomes difficult to set the leakage low-frequency electric field within the reference value range of the TCO standard, as the size of the liquid crystal panel becomes larger. In the case where the dot inversion driving is used, the reference signal a steady signal, and hence the voltage of the reference signal that is supplied to a component on the counter substrate is not changed, and hence it is expected that the leakage low-frequency electric field is weaker than that in the case where the line inversion driving is used. Therefore, the dot inversion driving is used in order to make the leakage low-frequency electric field lower.
As described above, in order to make the leakage low-frequency electric field lower, a prior art liquid crystal display device is configured so that a film for shielding an electromagnetic field is applied to a liquid crystal panel, or that an electrode for reducing electromagnetic field radiation and a unit for applying a voltage to the electrode are added to a liquid crystal panel. As a result, a process of producing the liquid crystal display device includes a step of attaching a member for attaining shielding of a leakage low-frequency electric field and circuit components accompanying the member, to the liquid crystal panel. Therefore, the number of production steps is larger than that in a process of producing an untreated LCD. Furthermore, the production yield of such a liquid crystal display device is lower than that of an untreated LCD. As a result, the production cost of the liquid crystal display device is higher than that of an untreated LCD. In the liquid crystal display device, the addition of the member for shielding a leakage low-frequency electric field and circuit components accompanying the member may cause the transmittance of the liquid crystal panel to be lower than that of an untreated LCD. Therefore, the liquid crystal display device is lower in display quality than an untreated LCD.
As described above, in order to set the leakage low-frequency electric field within the allowable range of the TCO standard, the prior art liquid crystal display device of the current structure uses the dot inversion driving technique. A driver for the dot inversion driving is more complex in structure and production process than that for the line inversion driving, and requires a complicated production process. Therefore, a driver for the dot inversion driving is more expensive than that for the line inversion driving. In the prior art liquid crystal display device of the current structure which uses the dot inversion driving technique, the device cost is higher than that of an untreated LCD of the current structure. The prior art liquid crystal display device having the counter source structure is configured so that, when the dot inversion driving is to be performed, the gradation signal is supplied to a component on the counter substrate, i.e., the column electrodes, and hence a steady signal is never supplied to the component. In the prior art liquid crystal display device having the counter source structure, even when the driving technique is improved, therefore, it is difficult to suppress a leakage low-frequency electric field.
It is an object of the invention to provide a display device capable of reducing a leakage low-frequency electric field can be reduced while preventing an increase in production cost and impairment in display quality.
In a first aspect of the invention a display device comprising:
a panel section including a plurality of pixel electrodes which are arranged in a predetermined reference plane, a display medium layer consisting of a display medium whose state relating to a display is changed in accordance with an electric field, and a single common electrode which is opposed to all the pixel electrodes via the display medium layer;
gradation signal supplying means for supplying a gradation signal of a voltage which varies with time, to the respective pixel electrodes, in order to define the electric field for controlling the state of the display medium interposed between the pixel electrodes and the counter electrodes,; and
reference signal supplying means for supplying a reference signal of a voltage which varies in a predetermined pattern with time, to the common electrode,
a difference Vbpp between maximum and minimum voltages of the reference signal, being equal to or smaller than a first upper limit voltage difference VMAX1 which is defined by an area x [m2] of the common electrode as follows:
xe2x80x83VMAX1=0.3578xc3x97xxe2x88x920.6156[V]
According to the first aspect of the invention, the display device comprises the panel section in which the pixel electrodes are opposed to the single common electrode via the display medium layer, i.e., the panel section of the current structure, and the voltage difference Vbpp of the reference signal which is supplied from the reference signal supplying means of the display device to be applied to the common electrode is restricted to a value which is not more than 0.3578xc3x97xxe2x88x920.6156 [V] (wherein x is the area [m2] of the common electrode) and not less than 0 V. In the display device of the invention, therefore, a leakage low-frequency electric field caused by the reference signal and produced from the panel section in the device can be surely suppressed to the upper limit reference value of a leakage low-frequency electric field defined in the TCO standard or less, only by adjusting the voltage difference Vbpp of the reference signal. The structure and the production process of the panel section in the display device of the invention can be made identical with those of a panel section of the prior art. In the display device of the invention, therefore, a leakage low-frequency electric field from the panel section can be suppressed very easily, and increases of the production cost and the number of components of the panel section, and impairment of the yield which may be caused by a countermeasure for suppressing the leakage low-frequency electric field can be prevented from occurring.
In a second aspect of the invention it is preferable that the panel section further includes:
gradation signal lines interposed between the gradation signal supplying means and the pixel electrodes;
switching elements interposed between the gradation signal lines and the pixel electrodes, respectively; and
scanning signal lines for supplying an opening/closing signal to the switching elements to control an opening/closing state of each of the switching elements.
According to the second aspect of the invention, the display device has the same configuration as that of the display device according to the first aspect of the invention, and the panel section further includes the above-mentioned components. As a result, the panel section is formed as an active matrix panel section having the current structure. In the display device of the second aspect, therefore, a leakage low-frequency electric field caused by the reference signal and produced from the panel section which can display an image configured by a plurality of pixels can be surely suppressed to the upper limit reference value of a leakage low-frequency electric field defined in the TCO standard or less, only by adjusting the voltage difference Vbpp of the reference signal. Consequently, the display device according to the second aspect of the invention can be suitably used as an image display device for an information apparatus.
In a third aspect of the invention a display device comprises:
a panel section including a plurality of pixel electrodes which are arranged in a predetermined reference plane; a display medium layer consisting of a display medium whose state relating to a display is changed in accordance with an electric field; and a plurality of counter electrodes which are opposed to the pixel electrodes via the display medium layer, respectively;
reference signal supplying means for supplying a reference signal of a voltage which varies in a predetermined pattern with time, to all of the pixel electrodes; and
gradation signal supplying means for supplying a gradation signal of a voltage variable with time, to the respective counter electrodes in order to define the electric field for controlling the state of the display medium interposed between the pixel electrodes and the counter electrodes,
a difference Vspp between maximum and minimum voltages of the gradation signal, which is equal to or smaller than a second upper limit voltage difference VMAX2 which is defined by an area x [m2] of a predetermined display region where all the pixel electrodes can be arranged, and a ratio y of an area of all the counter electrodes to the area x of the display region as follows:
VMAX2=axc3x97xxe2x88x92b[V]
wherein
a=0.3565xc3x97yxe2x88x920.6829 
b=xe2x88x920.0937y+0.7091
According to the third aspect of the invention, the display device has the panel section in which pixel electrodes are opposed to the counter electrodes via the display medium layer, respectively. In the liquid crystal panel having the above-mentioned structure, the structure of portions relating to the pixel electrodes and components disposed in the periphery of the pixel electrodes is simpler than that of a liquid crystal panel having the current structure, and the production cost of the panel section is lower than that of a panel section having the current structure. The reliability of the panel section after production is improved. Furthermore, a component which is in the panel section having the above-mentioned structure, and to which an electric signal functioning as a main cause of a leakage low-frequency electric field is supplied is smaller in area than that which is in the panel section having the current structure, and to which an electric signal functioning as a main cause of a leakage low-frequency electric field is supplied. In the display device according to the third aspect of the invention, therefore, the leakage low-frequency electric field from the panel section can be reduced more easily than that in a display device having a panel section of the current structure.
In the display device according to the third aspect of the invention, the voltage difference Vspp of the gradation signal which is supplied from a gradation signal supplying section to be applied to the counter electrodes is restricted to a value which is axc3x97xxe2x88x92b [V] {wherein a=0.3565xc3x97yxe2x88x920.6829, b=xe2x88x920.0937y+0.7091, x is the area of the display region, and y is a ratio of the area of all the counter electrode to that of the display region} or less and not less than 0 V. In the display device, therefore, a leakage low-frequency electric field caused by the gradation signal and produced from the panel section of the device can be surely suppressed to the upper limit reference value of a leakage low-frequency electric field defined in the TCO standard or less, only by adjusting the voltage difference Vspp of the gradation signal. The structure and the production process of the panel section in the display device according to the third aspect of the invention can be made identical with those of a panel section of the prior art having the above-mentioned structure. In the display device according to the third aspect of the invention, therefore, a leakage low-frequency electric field from the panel section can be suppressed very easily, and increases of the production cost and the number of components of the panel section, and impairment of the yield which may be caused by a countermeasure for suppressing the leakage low-frequency electric field can be prevented.
In a fourth aspect of the invention a display device comprises:
a panel section including a plurality of pixel electrodes which are arranged in a predetermined reference plane, a display medium layer consisting of a display medium whose state relating to a display is changed in accordance with an electric field, and a plurality of counter electrodes which are opposed to the pixel electrodes via the display medium layer, respectively;
reference signal supplying means for supplying a reference signal of a voltage which varies in a predetermined pattern with time, to all the pixel electrodes; and
gradation signal supplying means for supplying a gradation signal of a voltage variable with time, to each of the counter electrodes in order to define the electric field for controlling the state of the display medium interposed between the pixel electrodes and the counter electrodes,
a difference Vdyn between a voltage between the pixel electrodes and the counter electrodes in the case where an electric field for setting the state of the display medium to a predetermined first state is defined, and a voltage between the pixel electrodes and the counter electrodes in the case where an electric field for setting the state of the display medium to a second state which is different from the first state is defined, being equal to or smaller than a third upper limit voltage difference VMAX3 which is defined by an area x [m2] of a predetermined display region where all the pixel electrodes can be arranged, and a ratio y of an area of all the counter electrode to the area x of the display region as follows:
VMAX3=axc3x97xxe2x88x92b[V]
wherein
a=0.3565xc3x97yxe2x88x920.6829
b=xe2x88x920.0937y+0.7091
According to the fourth aspect of the invention, the display device has the panel section in which pixel electrodes are opposed to the counter electrodes via the display medium layer, respectively. In the display device according to the fourth aspect of the invention, because of the same reason as that of the display device according to the third aspect of the invention, the structure of portions relating to the pixel electrodes and components disposed in the periphery of the pixel electrodes is simple, and the production cost of the panel section is lower than that of a panel section having the current structure. Furthermore, the reliability of the panel section after the production is improved. In the display device according to the fourth aspect of the invention, therefore, the leakage low-frequency electric field from the panel section can be reduced more easily than that in a display device having a panel section of the current structure.
In the display device according to the fourth aspect of the invention, the difference Vdyn of the voltages between the pixel electrodes and the counter electrodes for respectively defining two kinds of electric fields for setting the display medium in the panel section to two different kinds of states is restricted to a value which is axc3x97xxe2x88x92b [V] {wherein a=0.3565xc3x97yxe2x88x920.6829, b=xe2x88x920.0937y+0.7091, x is the area of the display region, and y is a ratio of the area of all the counter electrode to that of the display region} or lower and not less than 0 V. The difference Vspp between the maximum and minimum voltages of the gradation signal in the display device is always smaller than the upper limit VMAX3 of the difference Vdyn between the voltages for defining the electric field. In the display device according to the fourth aspect of the invention, therefore, a leakage low-frequency electric field caused by the gradation signal and produced from the panel section can be surely suppressed to the upper limit reference value of a leakage low-frequency electric field defined in the TCO standard or less, only by adjusting the configuration of the panel section for defining the difference Vdyn between the voltages for defining the electric field. The structure and the production process of the panel section in the display device according to the fourth aspect of the invention can be made identical with those of a panel section of the prior art having the above-mentioned structure. In the display device according to the fourth aspect of the invention, therefore, a leakage low-frequency electric field from the panel section can be suppressed very easily, and increases of the production cost and the number of components of the panel section, and impairment of the yield which may be caused by a countermeasure for suppressing the leakage low-frequency electric field can be prevented from occurring.
In a fifth aspect of the invention, it is preferable that the panel section further includes gradation signal lines which are interposed between the gradation signal supplying means and the counter electrodes, and reference signal lines which are interposed between the reference signal supplying means and the pixel electrodes, and the gradation signal lines are disposed in a relation of skew position with respect to the reference signal lines, respectively.
According to the fifth aspect of the invention, the display device has the same configuration as that of the display device according to the third or fourth aspect, and the panel section further includes the above-mentioned components. As a result, the panel section is formed as a so-called active matrix panel section. When an arbitrary gradation signal line and all opposed electrodes connected to the gradation signal line are integrated with one another and an arbitrary reference signal line and all pixel electrodes connected to the reference signal line are integrated with one another, the panel section is formed as a so-called simple matrix panel section. In the display device according to the fifth aspect of the invention, therefore, a leakage low-frequency electric field caused by the gradation signal and produced from the matrix panel which can display an image configured by a plurality of pixels can be surely suppressed to the upper limit reference value of a leakage low-frequency electric field defined in the TCO standard or less, only by adjusting the voltage difference Vspp of the gradation signal or the difference Vdyn between the voltages for defining the electric field. Consequently, the display device according to the fifth aspect of the invention can be suitably used as an image display device for an information apparatus.
In a sixth aspect of the invention, it is preferable that the gradation signal lines and the counter electrodes connected thereto are integrated to form an electrically conductive portion, and an area per unit length of a first part of the electrically conductive portion is smaller than an area per unit length of a remaining part of the electrically conductive portion other than the first part, the first part being opposed to the reference signal lines.
According to the sixth aspect of the invention, the display device has the same configuration as that of the display device according to the fifth aspect of the invention, and the panel section is configured as described above. As a result, in the panel section of the display device according to the sixth aspect of the invention, an electrical shielding member which is opposed to the reference signal lines is reduced as compared with the panel section of the prior art in which the area per unit length of the first part is equal to that of the remaining part. As a result, the effect of canceling a leakage low-frequency electric field caused by the reference signal in the panel section in the display device according to the sixth aspect of the invention is greater than that of canceling a leakage low-frequency electric field caused by the reference signal in the panel section of the prior art. Consequently, a leakage low-frequency electric field caused by the gradation signal lines and produced from the panel section of the display device according to the sixth aspect of the invention is further reduced as compared with a leakage low-frequency electric field of a liquid crystal display device including the panel section of the prior art.
As a result, the cross capacitance of the first part in the panel section of the display device according to the sixth aspect of the invention is smaller than that of the first part in the panel section having the counter source structure of the prior art. In the display device according to the sixth aspect of the invention, therefore, delays of the gradation signal and reference signal are reduced in degree as compared with the case of the panel section having the counter source structure of the prior art. Because of these reasons, the display device according to the sixth aspect of the invention can be made higher in display quality than the prior art display device including a panel section having the counter source structure.
In a seventh aspect of the invention, it is preferable that the electrically conductive portion has a substantially strip-like shape, and a hole is opened in the first part in the electrically conductive portion.
According to the seventh aspect of the invention, the display device has the same configuration as that of the display device according to the sixth aspect of the invention, and the electrically conductive portion is configured as described above. As a result, in the panel section of the display device according to the seventh aspect of the invention, parts in the conductive portion and located on the both sides of the first part are connected to each other through a plurality of film pieces which remain in the first part of the electrically conductive portion. In the case where any one of the plurality of film pieces in the first part is broken, therefore, the two remaining parts are electrically connected to each other through remaining parts. Namely, in this case, the electrically conductive portion is hardly broken. This is preferable.
In an eighth aspect of the invention, it is preferable that the panel section further includes a plurality of switching elements which are interposed between the reference signal lines and the pixel electrodes, respectively, and scanning signal lines for supplying an opening/closing signal to the switching elements to control an opening/closing state of each of the switching elements, and the scanning signal lines are disposed in a relation of skew position with respect to the gradation signal lines, respectively.
According to the eighth aspect of the invention, the display device has the same configuration as that of the display device according to the fifth aspect of the invention, and the panel section further includes the above-mentioned components. As a result, the panel section is formed as an active matrix panel section having the so-called counter source structure. In the display device according to the eighth aspect of the invention, therefore, a leakage low-frequency electric field caused by the gradation signal and produced from the panel section which can display an image configured by a plurality of pixels can be surely suppressed to the reference value of a leakage low-frequency electric field defined in the TCO standard or less, only by adjusting the voltage difference Vspp of the gradation signal. Consequently, the display device according to the eighth aspect of the invention can be suitably used as an image display device for an information apparatus.
In a ninth aspect of the invention, it is preferable that the gradation signal lines and the counter electrodes connected thereto are integrated to form an electrically conductive portion, and an area per unit length of a second part of the electrically conductive portion is smaller than an area per unit length of a remaining part of the electrically conductive portion other than the second part, the second part being opposed to the scanning signal lines.
According to the ninth aspect of the invention, the display device has the same configuration as that of the display device according to the eighth aspect of the invention, and the panel section is configured as described above. As a result, the area of the second part in the electrically conductive portion of the panel section according to the ninth aspect of the invention is smaller than that of the second part in the panel section having the counter source structure of the prior art. Therefore, a leakage low-frequency electric field from the panel section of the display device according to the ninth aspect of the invention is further reduced. As a result, the cross capacitance of the second part in the panel section is smaller than that of the second part in the panel section having the counter source structure of the prior art. In the display device according to the ninth aspect of the invention, therefore, delays of the gradation signal and scanning signals are reduced in degree as compared with the case of the panel section having the counter source structure of the prior art. Consequently, the display device according to the ninth aspect of the invention can be made higher in display quality than the prior art display device including a panel section of the counter source structure.
In a tenth aspect of the invention, it is preferable that the electrically conductive portion has a substantially strip-like shape, and a hole is opened in the second part in the electrically conductive portion.
According to the tenth aspect of the invention, the display device has the same configuration as that of the display device according to the ninth aspect of the invention, and the electrically conductive portion is configured as described above. In the display device according to the tenth aspect of the invention, because of the same reason as that of the display device according to the seventh aspect, the electrically conductive portion is hardly broken, which is advantageous.
In an eleventh aspect of the invention, it is preferable that the display medium is a liquid crystal.
According to the eleventh aspect of the invention, the liquid crystal display device has the same configuration as that of the display devices according to the first to tenth aspects of the invention, and the display medium layer is formed by a liquid crystal. The panel section of the liquid crystal display device may be either of the so-called transmission type or the so-called reflection type. As a result, in the liquid crystal display device, the panel section is thinner and lighter, and smaller in power consumption than another display device such as a CRT. Furthermore, a leakage low-frequency electric field produced from the panel section can be suppressed to the upper limit reference value of the TCO standard or less. Consequently, the liquid crystal display device according to the eleventh aspect of the invention can be suitably used as an image display device for an information apparatus.